Solenoid operated two-way valves are well known in the prior art and, more particularly, valves of this type are known to be used to control the flow of fuel into a timing chamber of an electronically controlled unit injector to permit control over both the quantity and timing of fuel injected into the combustion chamber of an internal combustion engine.
U.S. Pat. No. 4,431,160 issued to Burt et al discloses such an electrically operated valve for use in unit injectors of the type illustrated in U.S. Pat. No. 4,281,792. The '160 valve includes a cup shaped valve element universally mounted on a stem operator for movement between open and closed positions. A spring element biases the operator toward the valve open position. An armature, mounted on the stem operator opposite the valve element is selectively attracted toward the stator of a solenoid to cause the valve element to move to its closed position whenever the solenoid coil is energized. Valves of the type disclosed in the '160 patent are required to operate at very high speed (fully open and fully closed in 2.5 seconds) and must operate to block fluid at very high pressure (25-30,000 psi). To achieve this very high speed, the '160 cup shaped valve element must be arranged close to the valve seat as possible while providing adequate flow volume capacity. Such requirements necessitate extremely accurate positioning of the valve element relative to its valve seal.
When closed, valves of the type disclosed is the '160 patent must create a very tight seal and thus the valve element is mounted by a self-aligning assembly. To allow for the accurate adjustment noted above, the self-aligning assembly includes a nut threadingly engaged with the stem operator so as to properly position the valve element. The nut includes an upper spherically shaped surface which is in constant contact with a conically shaped lower surface of the cup-shaped valve element. The axial spacing between the valve element and the valve seat defines the stroke length of the valve and it is critical that this spacing be maintained at a predetermined optimum value. Fluctuation in this spacing of as little as 0.002 inches can affect the metering and timing of the injector and may eventually result in unacceptable performance of the injector, necessitating expensive repair. This fluctuation arises due to repeated impacts caused by reciprocation of the valve element between its open and closed positions.
Therefore, it is essential that the nut, which retains the cup-shaped valve element of the valve, be fixed in its predetermined optimum position and that this position be maintained throughout the life of the injector. In the above mentioned U.S. Pat. No. 4,431,160, it is the internal threads which are relied upon to act on the nut to hold the nut in place. This, however, has not been found to be reliable due to the above-mentioned constant reciprocation of the cap and nut. During this constant reciprocation, the valve will vibrate, which, in turn, will cause the adjustment nut to slip or rotate, thereby deviating from the preset optimum position which may result in failure of the valve and costly repairs.
One solution to the above-mentioned problem is that shown in FIG. 4 of the drawings. FIG. 4 illustrates a solenoid operated control valve 102 for controlling the flow of fuel essentially identical to that disclosed above. Here, however, it should be noted that the adjustment nut 104 is of a two-piece construction. The first piece being a through hole nut 106, open at both ends, which threadingly receives the stem member 108, and a circular cap 110 including a blade 112 which extends into a cooperating slot 114 formed in the end of the piston. Once the through hole nut 106 is set in its predetermined position, the cap 110 is welded thereon so as to mate the blade 112 within the cooperating slot 114 to restrain the nut from rotating relative to the piston. However, in practice, the blade and slot design includes built in clearances which must be provided so as to allow the blade to be inserted into the slot. Such clearances immediately result in fluctuations in the stroke, and repeated actuation of the valve gradually deteriorates this arrangement to a point where the stroke shift reaches an unacceptable value and results in failure of the injector. Such a design may also lead to unnecessary leakage due to either failure of the weld or an initial imperfect weld.
In addition to the problems associated with the clearances discussed above, during the welding process, excessive amounts of heat may be generated, resulting in the undesirable expansion and contraction of the metallic members of the valve. This expansion and contraction can result in a change in the optimum positioning of the valve closure element, a change which may be greater than 0.002 inches which can lead to critical inaccuracies in the injector.
The plunger assembly disclosed in U.S. Pat. No. 3,820,213 issued to Kent includes a shaft having a stem formed of a plastic or rubber-like material inserted therein. The stem is inserted into the shaft until a seat abuts against the end of the shaft and to secure the stem to the shaft a diametrical hole is drilled through the shaft and the stem for the insertion of a pin. The stem is later positioned in place on the seating surface and subjected to a temperature of 130.degree. C. which causes the tip of the stem to form to that shape of the seating face. The pin is provided merely to maintain the axial placement of the stem within the plunger. Neither the stem, plunger or pin are subjected to excessive internal pressures, nor is the maintenance of the positioning of the stem relative to the plunger critical in this environment.
A piston and rod assembly is disclosed in U.S. Pat. No. 3,489,442 issued to Wright and includes a first rod which is threaded part way into one end of a threaded axial bore in a piston and a second rod which is threaded into the other end of the axial bore of the piston until it contacts the first rod. At this point, a predetermined torque is applied to one of the rods, urging the ends of the rods into engagement with each other, which, in turn, prestresses the threads on the first and second rods against the threads of the threaded axially bore. To prevent movement of one of the rods relative to the other and relative to the piston, a transversely extending hole is drilled through the piston at a point where the hole will intercept the intersection of the first and second rods and a pin is inserted into this hole to prevent any relative rotational movement. Again, neither the rods nor the pins are subjected to internal pressures, nor is the positioning of the piston critical in this environment to the point where a fluctuation of 0.002 inches can result in failure of the assembly.
Clearly, there is the need for an adjustment and locking mechanism which will both accurately and reliably position a fluid valve closure element in a predetermined optimum position, and do so without resulting in any leakage of fluid from within the assembly.